Particles within an acoustic focusing chamber (or acoustic flow cytometer) can be separated from other components in a solution using acoustic force manipulation. See e.g., U.S. Pat. No. 7,340,957 issued Mar. 11, 2008, which is incorporated by reference. Particles exposed to an ultrasonic standing wave field will experience an average drift force positioning them at local pressure potential minima within an acoustic radiation pressure force potential. See e.g., US Patent Application Publication No. 2008/0245709, published Oct. 9, 2008, which is hereby incorporated by reference. The ability of ultrasonic radiation to separate particles derives from the particles' density/compressibility ratio. The density/compressibility contrast between particles and their host medium will determine the positioning of the particles under acoustic radiation exposure. Positive acoustic contrast particles that have a density/compressibility ratio greater than the surrounding medium will be positioned at local pressure potential minima nodes along the center of the focusing chamber (focused). Conversely, negative acoustic contrast particles with a smaller density/compressibility ratio than the surrounding medium will be positioned at local pressure potential minima antinodes along the side of the focusing chamber. After this positioning, positive acoustic contrast particles can be removed from the acoustic focusing chamber, leaving behind only negative acoustic contrast particles which can subsequently be focused to the center of the chamber for analysis.
Elastomers are long chained polymers that can be crosslinked to form elastic rubber. As a result of this crosslinked arrangement, elastomers distribute applied forces equally throughout the entire structure. This intrinsic attribute allows crosslinked elastomers to be compressed with an applied force or stress and recoil back to their original configuration without degradation occurring. This intrinsic mechanical property allows elastomeric particles to be used in applications requiring particle separations, concentrations, or manipulations using acoustic radiation pressure fields.
As described in the '709 patent application publication, most biological particles in aqueous solutions appear to exhibit positive acoustic contrast. Acoustic force manipulation has been used in the past to concentrate (focus) Chinese hamster cells, red blood cells, bacteria, fungal spores, and other types of biological particles in aqueous solution. See the '709 publication as well as Goddard, et al., Analytical Performance of an Ultrasonic Particle Focusing Flow Cytometer; Anal. Chem. (79), 8740-8746 (2007). Exploiting this property, acoustic radiation can be used to trap elastomeric negative acoustic contrast particles or separate them from many biological components within aqueous or unmodified biological samples. The '709 publication provides several examples of how this property, when combined with acoustic flow cytometry, can result in a powerful bioanalytical methodology.